In particular the invention relates to an improved brace for externally supporting and protecting the human ankle and subtalar joints from injury or re-injured during recreational pursuits or in correction or rehabilitation of pathological or congenital malalignments and injury. The invention also relates to improvements in a reusable external prophylactic support or brace for the human ankle joint.
A number of techniques and devices have been proposed by which ankle injury might be minimized or prevented. Before these techniques and devices can be discussed it is useful in first discussing the anatomy of the ankle.
The ankle and foot complex consists of twenty-eight bones including the tibia and fibula. This specification will deal primarily with the six bones which comprise the ankle, subtalar, and transverse tarsal joints.
The complex interactions between bones, ligaments, tendons and their musculature enable the foot to transfer from a mobile adaptor during ground interface to a rigid lever for propulsion. The body requires a flexible foot to accommodate the variations in the external environment, a semi-rigid foot that can act as a spring or lever arm for push off during gait and a rigid foot to enable body weight to be carried with adequate stability. The position of the subtalar joint is the major factor in this adaptation. Eversion of the calcaneus results in pronation of the subtalar joint which in turn "unlocks" the transverse tarsal joint-whilst inversion leads to supination of the subtalar joint which in turn "locks" the transverse tarsal joint creating a rigid forefoot. A thorough understanding of the interrelation between joint axes and planes of motion is essential to analysis of compensatory motion as a consequence of pathological or restricted motion.
The bones of the foot interlock to form three distinct arches. The medial and lateral longitudinal arches and the transverse arch. The formation of these arches allows the support of body weight with the least expenditure of anatomical material and provides protection of the nerves and vasculature of the plantar foot. The bones of the medial arch are passively interlocked by the plantar aponeurosis, the long and short plantar ligaments, and the plantar calcaneonavicular (spring) ligament. During weight bearing, and heel raise, tension is increased especially in the plantar aponeurosis as the metatarsophalangeal joint extends adding stability.
The shape of the articular surfaces is particularly important to the evaluation of components of joint motions. Ligaments guide and check excessive joint motion with fiber direction determining what motions are guided and limited. The dorsal surface of the talus is called the trochlea. It is convex anterior-posterior, and convex-concave-convex medial to lateral. The trochlea has been described as a section of a cone with its base on the medial side. This surface articulates with the reciprocally shaped distal tibia. The lateral aspect of the talus is flat and is directed slightly medially from anterior to posterior and articulates with a reciprocally shaped distal fibula. The talus is slightly wider anteriorly than posteriorly.
The distal tibiofibula joint forms a deepened joint called the ankle mortise. The ligaments which stabilize the ankle consist of the strong medial ligament, and the three bands of the lateral ligament, together with the lateral malleolus provide lateral stability to the ankle joint and stabilize the talus within the ankle mortise.
Rotary stability in a horizontal plane is provided by tension in the collateral ligaments, by compression of the talar facets against the malleoli and, in the loaded state, by the shape of the articular surfaces. The horizontal components of tension in the collateral ligaments form a ring resisting rotation by tension in opposing pairs. The primary function of the malleoli as far as stability is concerned, is to serve as pillars so that the collateral ligaments are close to the ankle axis and hence permit plantar-dorsiflexion. Rotary instability may be an additional factor in patients whose symptoms persist after injury to the lateral ligaments.
The transverse tarsal joint exhibits triplanar motion and consists of the talonavicular and calcaneocuboid joints. Motion perpendicular to the two axes may be independent of each other, but both are dependent upon the position of the subtalar joint.
The calcaneocuboid axis lies close to the longitudinal axis and is directed anteriorly and superiorly 15 degrees to the horizontal and 9 degrees to the longitudinal, whilst the calcaneonavicular joint is oblique, directed anteriorly and superiorly at 52 degrees to the horizontal and medially at 57 degrees to the longitudinal axis.
During activity, as a person lands from a jump, the ankle is plantar flexed. The three lateral ligaments and peroneal muscle provide the primary restraints to ankle inversion. As inversion proceeds and the strength of the peroneal muscle is overcome, injury to the lateral ligaments will occur as the range of motion of the talus in the ankle mortis is exceeded.
Injury to the lateral ligaments occurs in a progressive fashion. The anterior talofibular ligament being the first to be injured. If inversion continues the calcaneofibular ligament is the next to be injured and finally, in severe cases, the posterior talofibular ligament is torn. The other mechanism of ankle injury is eversion. Eversion injury is more severe than inversion injury and may lead to chronic ankle instability.
Previous devices such as taping strapping and semi-rigid orthosis have been proposed for supporting these joints by rigidly (or semi-rigidly) inhibiting motion in the direction of possible injury. The ankle is prone to the following types of injury: inversion, eversion, dorsi flexion sprains and plantar flexion sprains.
Strapping of the ankle has been used to support the ankle. This involves taping of the ankle with non-elastic adhesive tape. Cloth wraps, elastic wraps and elastic adhesive materials have also been used. Whether taping, regardless of material used, is effective is debatable. Tape initially provides restriction of motion but this diminishes as exercise progresses. Taping is effective in preventing ankle sprains. Tape is not reusable and for taping to be effective the ankle may need to be retaped which involves unwinding and re-winding of the tape which is time consuming and expensive.
Ankle supports or braces which are re-usable have attempted to support the ankle by rigidly or semi-rigidly inhibiting motion in the direction of possible injury.
Australian patent specifications 19364/88 and 65560/90 are typical of such earlier braces or supports. These devices generally attempt to prevent ankle injury by restricting the range of movement of the ankle and, because of their rigid construction the degree of restriction provided by these devices does not change significantly following exercise.
Also typical of earlier devices are those disclosed in U.S. Pat. Nos. 4556054, 4982733, 1666290, 4977891 and 4753229.
It is an object of the present invention to provide an ankle brace which at least minimizes the disadvantages referred to above.